They are harder to eat with because things (especially noodles) slip and slide off of them. They're good to stabfood with (even if doing that does make me look like an uncouth barbarian.) I've got a chopsticks-and-spoon set that I take around because they are convenient to carry and will never break.

I'm surprised that no one else has mentioned that one of the reasons Koreans use the flat, metal chopsticks instead of the square, wooden Japanese ones or the round, wooden Chinese ones is that metal chopsticks make effective thrown weapons, if the Japanese (or anyone else) suddenly decide to invade your country in the middle of dinner.

Korea has three main martial arts. The well-known tae kwon do of course, but also the lesser known arts of gumdo (sword fighting) and one called hapkido that somewhat similar to jujitsu, from what I've heard. This last one is the one you want to study if you want to learn how to throw a chopstick with lethal force.

I have not gone to a hapkidodojo to see someone do this in person, but after feeling these chopsticks in my hand (I eat with them every day), I do not find it the slightest bit hard to believe that a properly trained person could easily kill someone from across the room with one of these.

Although, as I said, I've never seen it done, I've had someone demonstrate the basic motion. The chopstick is held flat against the palm of the hand, with the base of the chopstick aligned with the bottom of the palm. The thumb crosses the palm to hold it in place, and the tip of the chopstick extends beyond the middle finger. The hand is raised above the head, palm inwards, elbow at about 90 degrees. The arm is swung downwards and elbow extended. The wrist is snapped, and the chopstick released when it is pointing at the target.

Being Korean, my family uses them at home all the time, unless a small number of guests are coming (in which case we break out the SILVER chopsticks) and when there are a large number of guests/children (in which case we just use wooden ones). They are not found easily at restaurants, but it seems that the majority of Koreans use them.

As eric+ said before, it is different than using wooden chopsticks. First of all, you cannot leave them in very hot soup for more than a couple of minutes, or else they will get hot and will be hard to pick up. I, having used them all my life, find them easier to use than the wooden variety, but I understand how they might be more difficult. It is harder to use good chopstick form when using them.

They are indeed good for stabbing things. I do it all the time (I'm not sure about how often others do it) with flat, stacked, soft foods.

I'm not sure about why people started using metal chopsticks, but they do have some advantages, including:

Easy to clean

Long-lasting

Easy to mass-produce

As for the "proper usage" issue, a gringo could learn to use chopsticks better than I in a couple of minutes, and get used to it in a week.